1. Field of the Invention
The present invention generally relates to the field of fabricating integrated circuits, and more particularly relates to a method and apparatus for cleaning semiconductor wafers.
2. The Related Art
During the integrated circuit fabrication process, a wet cleaning process is essential for obtaining high quality integrated circuits. After a dry etching process, a wafer needs to be cleaned to remove residual photoresist, organics produced during the dry etching process, and film material attached on a surface of the wafer. The main chemical solution for cleaning the wafer includes, for example SC1, BOE and SPM which is a mixture of H2SO4 and H2O2. Thereinto, the temperature of SPM is higher than 90° C. and the SPM is used for removing the residual photoresist and organics. Generally, there are two ways to clean the wafer in the industry. One is batch cleaning and the other is single wafer cleaning, both of which will be comparatively described.
The batch cleaning is capable of cleaning a plurality of wafers every time. An apparatus for batch cleaning includes mechanical transmission devices and several cleaning tanks. A plurality of wafers can be cleaned in one of the cleaning tanks simultaneously, so the efficiency of batch cleaning is high and about four hundred wafers can be cleaned per hour. Moreover, because the chemical solution in the cleaning tanks is circulated, therefore, the chemical solution can be reused and the cost of batch cleaning is reduced, especially for high temperature chemical solution, like 120° C. SPM, for the high temperature SPM is expensive, so the cleaning cost can be reduced by using the batch cleaning. However, with the line width of integrated circuit shrinking continuously, the disadvantages of the batch cleaning are exposed visibly. During the batch cleaning process, the wafers are put in the cleaning tanks vertically, which easily causes cross contamination. Specially, if one of the wafers in one of the cleaning tanks has metal or organic contaminants, all the wafers cleaned in the same cleaning tank are contaminated. After cleaned, the wafers are taken out of the cleaning tanks vertically. At this time, if the chemical solution in the cleaning tanks has some tiny organic contaminants, the tiny organic contaminants will adhere to the surfaces of the wafers along with the chemical solution. Once the wafers are dried, the tiny organic contaminants on the wafers are very hard to remove.
The single wafer cleaning can only clean a piece of wafer every time. An apparatus of single wafer cleaning includes mechanical transmission devices and several independent single wafer cleaning modules. The cleaning and drying processes of one wafer are finished in one single wafer cleaning module. After cleaning a piece of wafer, the chemical solution in the single wafer cleaning module is drained and new chemical solution is supplied to the single wafer cleaning module to clean another piece of wafer, avoiding cross contaminant. The single wafer cleaning can effectively remove particles and film material, but the single wafer cleaning has a limitation in use of high temperature chemical solution, such as SPM which temperature is higher than 90° C., because the high temperature chemical solution is hard to recycle.
Both the batch cleaning and the single wafer cleaning have their own advantages and disadvantages. Only adopting the batch cleaning or the single wafer cleaning cannot achieve the best cleaning effect and also cannot meet the needs of modern process. Therefore, inventing a new method and apparatus which combine the advantages of the batch cleaning and the single wafer cleaning will be a great contribution to the integrated circuit fabrication process.